It is certainly useless.
And I would definitely not recommend seeking help on talk pages as new posts / comments can go easily unnoticed for a long time. Sending people to wiki discord is a way better option.

Such message is generally automatic though, like on fandom wiki.
I don't remember such thing being made here or any of the editors being appointed to greet new contributors. You have't even asked the staff if your template can look like that, spammed on people's comments in all cases or be created in the first place.

Template you wanted to create wasn't for personal purposes so you should get approval from wiki admins (like from petri or adlai). And that is before you even started using it. They aren't always online which means that you might have to wait few hours. In that time you shouldn't have had used it at all unless you wanted to post it on your own profile / sandbox / etc as they belong to your "private space".

Not everyone wants to have a welcome message, again, if something like this is even needed should be discussed with the staff. Such thing seemingly didn't exist here before and I think that it's great without it.

If you want to ask for such stuff, don't post it on normal contributor's talk pages. Chances you'll get anywhere like that are slim since they're not the people you should have asked. Dashi is not an admin, neither am I.

Please use wiki discussion instead of sending messages under my userpage. I outright thought this was spam from my boyfriend. That's how misplaced this is.
And about the Welcome page, that is something you should discuss with the actual leadership administration, not me. Consider me a moderator, if you will.